It's a strictly better Squelch 😱

I suppose it might be fine since Squelch hasn't seen that much competitive play over the years... though I mean there's the thing of introducing all the Stifle shenanigans into modern with this efficiency. Weirdly enough, Stifle is currently legal in historic, but not in modern.

I think it's fine. I might change it to a cycling ability for 3 mana like in Nimble Obstructionist and be on a spell of some sort. It has a lot of versatility, being an easy 2-for-1 on a cycling ability or stopping a mutate trigger.